[petsc-users] [petsc-maint] Issues linking petsc header files and lib from FORTRAN codes

[Barry Smith]

 Please send your attempted makefile and we'll see if we can get it working.

  I am not sure if we can organize the include files as Fortran compiler include files easily. We've always used the preprocessor approach. The Intel compiler docs indicate the procedure for finding the Fortran compiler include files https://www.intel.com/content/www/us/en/develop/documentation/fortran-compiler-oneapi-dev-guide-and-reference/top/program-structure/use-include-files.html is the same as for the preprocessor include files so I don't understand how the using the Fortran compiler include file approach would make the makefiles any simpler for users?


  Barry


> On Nov 3, 2022, at 8:58 PM, Jianbo Long <longtuteng249 at gmail.com> wrote:
> 
> Hello,
> 
> I'm struggling to make my FORTRAN code work with petsc as I cannot link the required header files (e.g., petscksp.h) and compiled library files to my FORTRAN code. 
> 
> Compiling petsc was not a problem. However, even with the fortran examples (see those on https://petsc.org/main/docs/manual/fortran/) and the guide on using petsc in c++ and fortran codes (see Section "Writing C/C++ or Fortran Applications" at https://petsc.org/main/docs/manual/getting_started/), I still cannot make my FORTRAN code work. 
> 
> The Fortran test code is exactly the example code ex83f.F90 (see attached files). Aftering following the 2nd method in the Guide (see the picture below), I still get errors:
> 
> petsc/finclude/petscksp.h: No such file or directory
> 
> Even if I set up the path of the header file correctly in my own makefile without using environment variables, I still can only find the file "petscksp.h" for my code. Of course, the trouble is that all other headers files required by KSP are recursively included in this petscksp.h file, and I have no way to link them together for my Fortran code. 
> 
> So, here are my questions:
> 1) in the Guide, how exactly are we supposed to set up the environment variables  PETSC_DIR  and PETSC_ARCH ? More details and examples would be extremely helpful !
> 2) Is there a way to get rid of the preprocessor statement 
>  #include <petsc/finclude/petscvec.h>
> when using c++/Fortran codes ?
> 
> For example, when using MUMPS package in a Fortran code, we can simply use compiler 'include', rather than a preprocessor, to extract all required variables for the user's codes :
>   INCLUDE 'zmumps_struc.h'
> where the header file zmumps_struc.h is already provided in the package. Similarly, I think it's much more portable and easier when using petsc in other codes if we can make it work to use petsc. 
> 
> (Note: similar issues were discussed before, see https://lists.mcs.anl.gov/mailman/htdig/petsc-users/2019-January/037499.html. Unfortunately, I have no clue about the solution archived there ...)
> 
> Any thoughts and solutions would be much appreciated !
> 
> Thanks,
> Jianbo Long
> 
> <image.png>
> <ex83f.F90>

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